In U.S. Pat. No. 4,099,427, there is disclosed a planetary gear with central wheels the plane tooth flanks of which mutually form virtual tooth gaps of substantially triangular shape. The teeth of a planet wheel being engaged in these virtual tooth gaps, they are in mesh with them across a large portion of the circumference, in the extreme throughout almost all of it. However, as the flank angles of the virtual tooth gaps are continuously varying across the circumference of the planetary gear, there is no warranty for positive face-to-face engagement across the entire circumference of the planet gear between (a) the tooth flanks of the plant wheel on the one hand and (b) the tooth flanks of the central wheels in the virtual tooth gaps on the other hand.
In order to overcome this problem, is has been proposed to design the teeth planet wheel such that the angles formed by their flanks are variable. In one type with identical central wheels having internal toothing, this is effected by making the corresponding external toothing of the planet wheel of zigzag-shaped sheet metal. In another type with the central wheels having external toothing, the planet wheel comprises individual teeth whose profile angles are variable under compliance so that the individual teeth adapt to the variable flank angles of the virtual tooth gaps. It has also been suggested to make the central wheel teeth pivotable to some extent by providing each of the central wheels with elongated recesses so that the foot of each tooth is connected to the central wheel body by a slender web that forms a joint which permits slight pivoting of the respective central wheel tooth.
By variation of the flank angles of the teeth of the planet wheel and/or of the central wheels, the gear types mentioned have thus solved the problem stated of providing for an adaptation to the varying flank angles of the virtual tooth gaps. However, problems continued to exist for two special applications:
(1) With low speed ratios from about 30 down to about 7, the variations of the flank angles of the virtual tooth gaps are so wide that the resilient tooth means of the planet wheel and/or of the central wheels as provided by the prior art have proven to be insufficient.
(2) The known resilient tooth means of the planet wheel and/or of the central wheels are less suited for the transmission of very large torques.